Only call pa_cvolme set on stream creation if volume explicitly set.

Streams without a custom volume set use suitable volume selected
by the PulseAudio server. This is usually the correct choice, since then
stream-restore module can apply old volume to the stream. Also with
Sailfish explicitly setting the volume to streams breaks system volume.

Change-Id: I75f5bf4e7aaafb4bd55510f5ac4ddf03767d494b
Done-with: Juho Hämäläinen <juho.hamalainen@tieto.com>
Reviewed-by: Andrew den Exter <andrew.den.exter@qinetic.com.au>

src/plugins/pulseaudio/qaudiooutput_pulse.h

@@ -142,6 +142,7 @@ private:
     QString m_category;
 
     qreal m_volume;
+    bool m_customVolumeRequired;
     pa_cvolume m_chVolume;
     pa_sample_spec m_spec;
 };